Well, that looks...highly irregular.
After giving it some thought, though, I remembered mentioning the song contest terms earlier. I wonder how much of a stretch it would be to think that the artwork in the coloring book was selected/compiled similarly?
If the two work the same way, CFM acquires certain rights of the original creators when a song is selected as a winner. They use those rights to actually let themselves include the song in the concert, as well as for promotional purposes. It's a little different from what I remember from the song contest I did, but
here's a page describing the Mirai 2021 song contest; near the bottom, if the machine translation is to be believed, it talks somewhat about the transfer of rights to CFM and about the original authors not exerting certain of their authorship rights against CFM or designated third parties, or something to that effect. Basically, I think it's saying that the original creators agree to let CFM/designated third parties do particular things with the song without suing them.
Also, have a look at the video from Eji from further down in that Tweet thread: on the left-hand page (which I assume refers to the current illustration; if it doesn't, I assume the same sort of message is likely present for most/every illustration in the book), it says "(c) Crypton Future Media, INC," right below the artist's name. If CFM has the copyright, they may have the ability to let Graphic India use that image, or any other Miku image to which CFM has similar rights, for promotional purposes. Basically, GI could be one of those designated third parties.
Not saying I know any of this to be true, but things may not be the clusterf**k they appear at first glance.
Usually, I think CFM always includes the name of the original artist in whatever artwork they use, though, though I'm not sure they technically HAVE to. Not sure why that wasn't done in this Tweet from Graphic India.